Gaseous discharge device



' Nov. 16, 1937. H FELE 2,099,111

GASEOUS DISCHARGE DEVICE Filed March 9, 1935 2 Sheets-Sheet l INVENTORJ. R. HEFELE A T TORNEV Nov. 16, 1937. HEFELE 2,099,111

GASEOUS DI SCHARGE DEVICE LAMP CURRENT IN M/LL/AMPERES FIG. 4

6 LIOHT- POWER CURVES V- A CATHODE HEATED CAT/ ODE COLD PHOTO-ELECTRICRESPONSE IN MICROAMPERES o a z a 4 s a 1 LAMP POWER //v WATTS lNl/ENTORJ. R. HE FELE ATTORNEY Patented Nov. 16, 1937 UNITED STATES PATENTOFFICE GASEOUS DISCHARGE DEVICE Application March 9, 1935, Serial No.10,239

10 Claims.

This invention relates to a gaseous discharge device and moreparticularly to a device having a heated cathode.

The prior'art contains a disclosure of a discharge lamp including acathode adapted to be heated to electron emitting temperature, in whichthe cathode is directly and continuously heated by electriccurrentsupplied by the source which supplies energizing potential to thedischarge l path or indirectly heated by supplying current from thatsource to a heating unit associated with a cathode either during thestarting period alone, i. e., for a short time preceding theinitiationof the discharge across the path between i the electrodes whenthe heating unit is disconnected from the supply source, or during astarting period and throughout the operating period.

While such a lamp is satisfactory for lighting purposes, it is notadapted for use in signaling 3 systems wherein the energy supplied tothe discharge path varies between wide limits of current and voltage,for the reason that at low values of current and voltage the lampbecomes inoperative, because the current supplied to the heat- 5 er isinsufiicient to maintain the cathode heated to electron emittingtemperatures, with the result that certain signals may be lost or somutilated that-they are unintelligible. Again, since the heat suppliedby the heater unit varies with p the square of the current, thetemperature of the cathode and hence its electron emissivity will varytherewith and, as a result, the signal produced will be distorted.

In certain types of signaling, such as in picture I transmission andtelevision systems and in sound recording, it is essential that thelight source be maintained in a continuously operative condition inorder that the light supplied by it may faithfully follow variations ofthe signal current and potential, which fluctuate from substantiallyzero amplitude, representing a dark condition or a minimum intensity, toa large amplitude corresponding to white or maximum intensity. In otherwords, the operation of the heating unit must be independent of thepotential producing the discharge between the electrodes.

An object of this invention is to provide a gaseous discharge lampadapted to be supplied with variable energizing potential and having a 0heated cathode, the temperature of which is independent of the potentialproducing the discharge.

Another object is to provide a gaseous discharge lamp adapted to besupplied with variable ener- 5 gizing potential and having a cathodecontinuously maintained at electron emitting temperature.

An important feature of this invention relates to a gaseous dischargedevice having a heating unit exposed to the discharge but protected frombombardment by such discharge.

According to one embodiment of this invention, a gas-filled container orbulb encloses electrodes between which is applied a signal br variablepotential for controlling a luminous dis- 1o charge between them. Theelectrodes comprise an anode having a small aperture, and either atubular cathode surrounding, or a. cylindrical cathode having a closedend adapted to completely enclose, a heating unit that is supplied withconstant current for maintaining the cathode at all times heated to anelectron emitting temperature. There is also a discharge directingmember provided with a capillary opening, this capillary opening and theaperture in the anode being in line with the longitudinal axis of thecathode, whereby there is provided a low voltage positive column gaseousdischarge device which operates to produce light which varies inintensity with the fluctuating signal potentials applied to itselectrodes and hence operates to faithfully reproduce the signalswithout introducing dis-' tortion.

A detailed description of the invention follows which is illustrated inthe attached drawings, in which Fig. 1 illustrates a glow lamp, partlyin section, having atubuiar cathode surrounding a heating unit;

Fig. 2 shows a glow lamp, also partly in section, in which the heatingunit is completely enclosed by a cathode;

Fig. 3 is a graphical representation of the relation between the voltageand the current applied to the lamp; and

Fig.4 is a graphical representation of the relation between the lightemitted and the power taken by the luminous discharge of the heatedcathode type lamp as compared with a cold cathode lamp of otherwisesimilar construction.

Referring more particularly to the drawings, Fig. 1 shows a glowdischarge lamp comprising a bulb I provided with a press 2. Lead-inconductors 3 and 4 extend through this press 2, conductor 3 connectingto one terminal of a heating unit or coil 5 while conductor 4 isconnected to cathode 6, to which the other terminal I of the heatingcoil 5 is attached for a purpose which will be more fully explained asthe description PIOQQQGSQ The cathode 6 in Fig. 1 comprises an opencylinder surrounding the heating coil I and is formed of or externallycoated with a material which is adapted to be heated to electronemitting temperature by that coil.

5 Surrounding the cathode I is a cylindrical member I provided with aconical extension I which terminates in a capillary opening l0 ad-Jacent an aperture II in the anode l2. Aperture II in the anode l2 andthe capillary opening I0 are in line with the longitudinal axis of thecylindrical cathode I.

Clamped on the press 2 are a pair of split sleeves II from which rods l4extend into the lamp away from the base. These rods support the member 8which surrounds the cathode 8.

Secured to the rods II are a pair of rods II provided at their upperends with insulators II from which extend short projections I'l. Theseshort projections I! are secured to the anode I2. The elements l6 serveto electrically insulate the rods II from the projections l1 and thesethree sets of elements combined with the rods I serve as supports forthe anode l2. A lead-in wire l8 extends through the base of the lamp andis connected to the anode l2.

The bulb I contains a charge of a rare gas, such as neon, helium, orargon, at a pressure of a few millimeters of mercury. It may beadvantageous also to have a charge consisting of a mixture of one ofthese gases and either nitrogen, hydrogen or mercury. The pressure ofthe gas charge may be between 5 and 10 millimeters of mercury and, inthe case where nitrogen or hydrogen is used, the nitrogen or hydrogenmay constitute from 2 to 5 per cent by volume of the charge. Whenmercury is used a smaller amoun would be suillcient.

The coil 5 is supplied with heating current from any constant currentsource, such as, for 40 example, the battery IS. The negative terminal20 of the source I! is connected to the cathode I by means of thelead-in wire 4 and the positive terminal is connected via the lead-inwire 3 to the coil 5. The coil I is thus supplied with constant currentof sufllcient value to maintain the cathode 6 heated at all times toelectron emitting temperature. This is an important feature of thisinvention.

The negative terminal of the battery i9 is also connected to thenegative terminal of a battery '2l, which has its positive terminalconnected through the secondary winding of a transformer 22 and lead Itto the anode l2. The primary winding of the transformer 22 is suppliedwith variable signal current transmitted over the circuit 23, forexample, with current varying as the tone values of a picture or objectscanned at a transmitting station of a picture transmitting ortelevision system. Battery 2i supplies a steady potential of sufllcientvalue to cause a luminous positive column discharge of constant lightintensity to occur across the space between the surface of the cathode Iand the anode l2. This positive ionic discharge occurs between the g5anode l2 and both surfaces, inside and outside, of the cathode 8. Forthis reason, the discharge is distributed over a greater area than ifthe closed end cathode is used. The concentrated beam is consequentlymore intense. As the heating coil I is in the path of the discharge,means 'which will now be described are provided to prevent the positiveions from causing destructive ent of this coil. The drop across theheating coil I is such that the potential difference between the lowerend of the coil I and the anode I2 is less than that across the battery2| which produces the luminous discharge. This coil, therefore, is notsubject to the highly destructive ionic bombardment due to the luminousdischarge which would materially reduce the useful life of the lamp asall portions of the coil except the end connected to the cathode arepositively polarized with respect to the cathode. If the battery It werereversed in polarity, the potential difference between the lower end ofthe coil I and the anode l2 would then be greater than that between theanode l2 and the cathode I and most of the discharge would occur betweenthe coil I and the anode l2, thus materially reducing the life of thecoil I. By utilizing an electron emitting surface of extended area, alarge current carrying capacity is assured, and by concentrating thedischarge into the capillary opening It, a positive column of greatbrightness and constant intensity is produced.

By properly selecting the potential of the battery 2|, signals varyingover 'an extremely wide range of values may be supplied by thetransformer 22 for superposition on that supplied by the battery withoutcausing the eifective potential applied to the lamp to be reduced belowits extinction voltage. However, even if the signals areof suchmagnitude as to reduce the voltage applied to the electrodes to a valuebelow the extinction voltage of the lamp, the luminous discharge will beimmediately restarted upon restoration of the breakdown voltage of thelamp, due to the fact that the cathode is maintained uniformly heated toelectron emitting temperature by current from the constant currentsource I! As shown in Fig. 3, the relation between the voltage andcurrent supplied to the lamp is linear, and the line representing thisrelation has a negative slope. For an otherwise similar cold cathodelamp the slope would be positive.

Fig. 4 shows light versus power curves A and B, which respectivelyrelate to a heated cathode lamp of the type described herein and to acold cathode lamp of otherwise similar construction. It will be observedthat the shape of curve A for the heated cathode lamp is somewhatsimilar to curve B for the cold cathode lamp. However, the amount oflight produced by a glow discharge lamp having a heated cathode isseveral times that produced by a lamp of this type provided with a coldcathode, which is identical in design and is operated under exactly thesame conditions, and this result is attained with an expenditure of onlya fraction of the electrical power used in a cold cathode lamp. Curve Ashows only the power taken by the luminous discharge, but the totalpower curve (tahng into account the power extended by the heater coil)would be parallel to and slightly to the right of A.

The design of lamp shown in Fig. 2 differs from 7 that of Fig. 1 solelyin the feature that the cathode I, instead of being an open cylindersurrounding the heating coil, consists of a solid cylindrical body 30having a central bore 3| which extends from one end 32 thereof to apoint intermediate its length, so as to provide an electron emittingelement having closed upper end 33.

The heating coil I is secured in this opening so that it is completelyenclosed by the cylindrical charge. In this case, the battery l9 may beconnected in either direction with respect to the heating coil. Asshown, the heating coil is connected between the lead-in wire 3 and thecathode 6, but it may be connected between the two lead-in wires 3 and 4or directly to the terminals of battery l9.

' From the preceding description, it will be apparent that thisinvention provides a low voltage, positive column discharge lamp,designed to have a long useful life, operable with low power input toprovide a discharge having high current density to produce illuminationof great intensity and controllable by signal potentials which vary overan extremely wide range of values, such as, for example, those used insound recording and at the receiving station of a picture transmissionor television system to control the production of a picture or image,without causing the positive column discharge to be interrupted in suchmanner that distortion would be introduced.

What is claimed is:

l. A gaseous discharge device comprising electrodes determining adischarge path between said electrodes, a discharge directing memberbetween said electrodes, means for heating one of said electrodes toelectron emission temperature, and means for supplying to said heatingmeans constant current, one terminal of said heating means beingconnected to the heated electrode and the other terminal beingpositively polarized with respect thereto.

2. A gaseous discharge device comprising electrodes, a dischargedirecting member between said electrodes, a unit exposed to thedischarge between said electrodes for heating one of said electrodes toelectron emission temperature, and means for supplying to said unitconstant current, one terminal of said unit being connected to theheated electrode and the other terminal being positively polarized withrespect thereto.

3. In combination, a transformer, connections from a source of signalpotential to the primary of said transformer, a glow lamp comprising ananode, a cathode, and a heating unit for said cathode, a source ofdirect current in series with the secondary of said transformer and thedischarge space between said anode and cathode, and a source'of constantcurrent for said cathode heating unit, one terminal of said heating unitbeing connected to the cathode and the other terminal being positivelypolarized with respect thereto.

4. A positive column gaseous discharge device comprising an anode, acathode having an open end adjacent said anode, a member surrounding asaid cathode provided with a capillary opening, an aperture in saidanode, said aperture and capillary opening being in line with thelongitudinal axis of the cathode, a unit exposed to the dischargebetween said anode and cathode for heating said cathode to electronemission temperature, and means for supplying to said unit constantcurrent, one terminal of said unit being at cathode potential and theother tenninal being positively polarized with respect thereto.

5. A positive column gaseous discharge device comprising an anode, acylindrical cathode, a member surrounding said cathode provided with acapillary opening to direct the discharge between said anode andcathode, means within said cathode for heating it to electron emissiontemperature, a source supplying signal potential between said anode andcathode, and a source supplying constant current to said heating means,one terminal of said heating means being at cathode potential.

6. A positive column gaseous discharge lamp comprising an anode, acathode, a cylindrical member surrounding said cathode, a conical capfor said cylindrical member, a capillary opening at the apex of saidconical cap, an aperture in said anode, said aperture and capillaryopening being in line with the longitudinal axis of the cathode, andmeans exposed to the discharge between said anode and cathode forheating said cathode to electron emission temperature, said heatingmeans having one terminal thereof connected to said cathode and itsother terminal pos itively polarized with respect thereto to preventionic bombardment of said unit.

'7. A positive column gaseous discharge device comprising an anode, acathode, a cylindrical member surrounding said cathode, a conical capfor said cylindrical member, a capillary opening at the apex of saidconical cap, an aperture in said anode, said aperture and capillaryopening being in line with the longitudinal axis of the cathode, meanscombined with said cathode for heating it to electron emissiontemperature, a source supplying signal potential between said anode andcathode, and a source supplying constant current to said heating means.

8. A gaseous discharge lamp comprising a glass bulb, a press in saidbulb, a plurality of split sleeves clamped on said press, an anode, acathode, a heating unit for said cathode, an aperture in said anode, acylindrical member having a conical cap and a capillary opening at theapex of said cap surrounding said cathode, said aperture and capillaryopening being in line with the longitudinal axis of the cathode, rodsfastened to said split sleeves for supporting said cylindrical memberand said anode, leads through said press to said cathode and heatingunit, and a lead to said anode.

9. A positive column gaseous discharge device comprising a glassenclosure, a press in said enclosure, an anode having an aperturetherein, a cathode, a heating unit for said cathode, a cylindricalmember having a conical cap and a capillary opening at the apex of saidcap surrounding said cathode, said aperture and capillary opening beingin line with the longitudinal axis of the cathode, means on saidpress'for supporting said anode, cathode, heating unit, and cylindricalmember, a source supplying constant current to said heating unit, and asource supplying signal potential between said anode and cathode.

10. An electric discharge device comprising a gas-tight receptaclecontaining a gas filling, an anode, a cathode, and electrical meansadjacent said cathode for heating it to cause it to emit electrons, saidanode, cathode and heating element being so disposed that when anelectric discharge occurs between said anode and cathode said heatingmeans is exposed to bombardment by positive ions, and means for limitingsaid bombardment of said heating means comprising means for maintainingthe potential of at least the major portion of said heating means morepositive than said cathode.

.JOHN R. HEFELE.

